1. Field of the Invention
The present invention relates to the art of axle/suspension systems for vehicles. More particularly, the invention relates to the art of trailing or leading arm beam-type air-ride axle/suspension systems for heavy-duty vehicles, such as tractor-trailers or semi-trailers, which cushion the ride and stabilize the vehicle during operation. Still more particularly, the invention relates to an axle/suspension system for gross axle weight rating (“GAWR”) applications greater than 23,000 lbs./axle, that incorporates a large diameter axle having a reduced wall thickness and a sleeve disposed about the axle at the axle-to-beam connection. The sleeve has an increased wall thickness as compared to prior art sleeves for large diameter axles, and includes an asymmetrical pair of weld windows generally located at the front and rear portions of the axle. The sleeve windows are positioned between the beam sidewalls, with the inboard and outboard edges of each window being relatively farther from the beam sidewalls than in prior art sleeve windows. The axle/suspension system reduces weight and efficiently reacts loads imparted on the axle/suspension system during operation of the vehicle, while maintaining the desired stiffness and durability of the axle/suspension system.
2. Background Art
The use of air-ride trailing and leading arm rigid beam-type axle/suspension systems has been very popular in the heavy-duty truck and tractor-trailer industry for many years. Air-ride trailing and leading arm spring beam-type axle/suspension systems also are often used in the industry. Although such axle/suspension systems can be found in widely varying structural forms, in general their structure is similar in that each system typically includes a pair of suspension assemblies. In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a subframe, and the suspension assemblies connect directly to the subframe. For those heavy-duty vehicles that support a subframe, the subframe can be non-movable or movable, the latter being commonly referred to as a slider box, slider subframe, slider undercarriage, or secondary slider frame. For the purpose of convenience and clarity, reference herein will be made to a primary frame, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle axle/suspension systems suspended from primary frames, movable subframes and non-movable subframes.
Specifically, each suspension assembly of an axle/suspension system includes a longitudinally extending elongated beam. Each beam is located adjacent to and below a respective one of a pair of spaced-apart longitudinally extending frame main members. More specifically, each beam is pivotally connected at one of its ends to a hanger which in turn is attached to and depends from a respective one of the frame main members of the vehicle. The beams of the axle/suspension system can either be an overslung/top-mount configuration or an underslung/bottom-mount configuration. For purposes of clarity hereinafter, a beam having an overslung/top-mount configuration shall be referred to as an overslung beam and a beam having an underslung/bottom-mount configuration shall be referred to as an underslung beam. An axle extends transversely between and typically is connected by some means to the beams of the pair of suspension assemblies at a selected location from about the mid-point of each beam to the end of the beam opposite from its pivotal connection end. The opposite end of each beam also is connected to a bellows air spring or its equivalent, which in turn is connected to a respective one of the frame main members. A brake assembly and shock absorber also are mounted on each of the beams and/or axle. A height control valve is mounted on the hanger or other support structure and is operatively connected to the beam in order to maintain the ride height of the vehicle. The beam may extend rearwardly or frontwardly from the pivotal connection relative to the front of the vehicle, thus defining what are typically referred to as trailing arm or leading arm axle/suspension systems, respectively. However, for purposes of the description contained herein, it is understood that the term “trailing arm” will encompass beams which extend either rearwardly or frontwardly with respect to the front end of the vehicle.
The axle/suspension systems of the heavy-duty vehicle act to cushion the ride and stabilize the vehicle. More particularly, as the vehicle is traveling over-the-road, its wheels encounter road conditions that impart various forces, loads, and/or stresses, collectively referred to herein as forces, to the respective axle on which the wheels are mounted, and in turn, to the suspension assemblies that are connected to and support the axle. In order to minimize the detrimental affect of these forces on the vehicle as it is operating, the axle/suspension system is designed to react or absorb at least some of them.
These forces include vertical forces caused by vertical movement of the wheels as they encounter certain road conditions, fore-aft forces caused by acceleration and deceleration of the vehicle, and side-load and torsional forces associated with transverse vehicle movement, such as turning of the vehicle and lane-change maneuvers. In order to address such disparate forces, axle/suspension systems have differing structural requirements. More particularly, it is desirable for an axle/suspension system to be fairly stiff in order to minimize the amount of sway experienced by the vehicle and thus provide what is known in the art as roll stability. However, it is also desirable for an axle/suspension system to be relatively flexible to assist in cushioning the vehicle from vertical impacts, and to provide compliance so that the components of the axle/suspension system resist failure, thereby increasing durability of the axle/suspension system.
One type of prior art axle/suspension system and axle-to-beam connection is shown, described and/or claimed in U.S. Pat. No. 5,366,237, and is owned by the assignee of the present invention. This axle/suspension system provides a means for rigidly connecting the axle to the beam through a connection that substantially surrounds the axle, thereby preventing the axle from assuming a cross-sectional configuration substantially different from its manufactured unaltered cross-sectional configuration due to torsional forces. In one embodiment of the invention shown, described and/or claimed in the '237 patent, the means for rigidly connecting the axle to the beam includes an orifice formed in each of the beam sidewalls. Each orifice substantially surrounds both the axle, which extends through the orifices, and a sleeve that substantially surrounds and is rigidly attached to the axle. The sleeve in turn is rigidly attached to the beam through the orifices in the beam. The sleeve includes a pair of windows into which a continuous weld is laid in order to rigidly attach the sleeve to the axle. These windows are located on the front and rear portions of the axle. Moreover, these windows are generally symmetrical with respect to one another in size, shape and orientation relative to the horizontal centerline of the axle at vehicle design ride height, which is the height when the vehicle is not operating. A weld is laid circumferentially around the axle between the sleeve and each beam sidewall at the sidewall orifice in order to rigidly attach the axle to the beam.
Although the structure shown, described and/or claimed in the '237 patent can be used on standard diameter axles, in order to achieve reduced weight of the axle/suspension system it is desirable to utilize an axle having a larger diameter and thinner wall. Such large diameter axles, as they are generally known in the heavy-duty vehicle industry, have an outer diameter of about 5.75 inches as compared to an outer diameter of about 5.0 inches for standard axles. However, for such large diameter axles to be successfully utilized in the axle/suspension system, they must still be capable of meeting certain durability and stiffness requirements as generally defined in the heavy-duty vehicle market. Durability of the axle/suspension system generally refers to the ability of the system to resist wear and tear during operation of the vehicle, thus allowing the axle/suspension system to perform over an extended period of time without exhibiting wear and tear such as fatigue cracking of the welds or cracking of the axle itself during operation of the vehicle. Stiffness generally refers to the rigidity or firmness of the axle and is desirable because stiffness of the axle generally results in a more even distribution of the forces imparted on the axle/suspension system during operation of the vehicle.
Prior art axle/suspension systems utilizing large diameter axles and having relatively thin walls have been utilized successfully for axle/suspension systems having a GAWR of less than or equal to about 23,000 lbs./axle. The GAWR of a given axle/suspension system is determined by the manufacturer of the axle/suspension system and is generally defined as the load carrying capacity of a single axle/suspension system as measured at the tire-ground interfaces. GAWR can vary by manufacturer but GAWR of less than 20,000 lbs./axle, 20,000-23,000 lbs./axle and greater than 23,000 lbs./axle have become relatively standard market segments in the heavy-duty vehicle industry. No known large diameter axle having a relatively thin axle wall thickness has been successfully utilized in an axle/suspension system having a GAWR of greater than 23,000 lbs./axle.
The axle/suspension system of the present invention utilizes a large diameter axle having a relatively thin axle wall, yet the system is capable of maintaining the requisite stiffness and durability for the GAWR greater than 23,000 lbs./axle heavy-duty vehicle market. This desirable result is accomplished by: 1) utilizing a sleeve at the axle-to-beam connection having an increased wall thickness as compared to prior art large diameter axle sleeves; 2) forming and locating the front and rear windows in the axle sleeve with the inboard and outboard edges of each window being relatively farther from the beam sidewalls than in prior art sleeve windows; 3) forming and locating the front and rear windows so that they are asymmetrical with respect to one another in size, shape and/or location, as compared to relevant prior art axle/suspension systems. More specifically, the front window is generally larger and shaped different than the rear window, and the windows are asymmetrically angled with respect to the horizontal centerline of the axle at design ride height. The aforementioned structural changes decrease weight while maintaining durability of the axle/suspension system and maintaining the required stiffness of the axle/suspension system in order to efficiently react the forces imparted on the axle/suspension system during operation of the vehicle.